Tissue expanders are an important and integral part of reconstructive surgery. They are used to expand and increase the skin, or mucosa, to eventually allow the surgeon to reconstruct lost tissues. S. R. Baker, “Fundamentals of expanded tissue,” Head Neck, (1991) 13(4): 327-33. Tissue expanders have been used in the head, face, neck (H. Jhuma, et al., “Repair of a cheek defect with the tissue expander method: A case report,” Bull. Tokyo Dent. Coll., (1997) 38(4): pp. 311-316; O. Antonyshyn, et al., “Tissue expansion in head and neck reconstruction.” Plast. Reconstr. Surg., (1988) 82(1): pp. 58-68; J. B. Wieslander, “Tissue expansion in the head and neck: A 6-year review,” Scand. J. Plast. Reconstr. Surg., (1991) 25(1): pp. 47-56; J. T. Chun and R. J. Rohrich, “Versatility of tissue expansion in head and neck burn reconstruction,” Ann. Plast. Surg., (1998) 41(1): pp. 11-16; and S. E. MacLennan, et al., “Tissue expansion in head and neck burn reconstruction,” Clin. Plast. Surg., (2000) 27(1): pp. 121-132), chest wall (R. Newman and D. C. Cleveland, “Three-dimensional reconstruction of ultrafast chest CT for diagnosis and operative planning in a child with right pneumonectomy syndrome,” Chest, (1994) 106(3): pp. 973-974), scapula, shoulder, forearm (V. I. Sharobaro, et al., “First experience of endoscopic implantation of tissue expanders in plastic and reconstrucuve surgery,” Surg. Endosc., (2004) 17(12) p. 513-517), ear (B. S. Bauer, “The role of tissue expansion in reconstruction of the ear,” Clin. Plast. Surg., (1990) 17(2): pp. 319-325), finger (R. L. Simpson and M. E. Flaherty, “The burned smallfinger,” Clin. Plast. Surg., (1992) 19(3): pp. 673-682), hairline (R. Silfen, et al., “Tissue expansion for frontal hairline restoration in severe alopecia in a child,” Burns, (2000) 26(3): pp. 294-297), lumbosacral, perineum (T. O. Acarturk, et al., “Reconstruction of difficult wounds with tissue-expanded free flaps,” Ann. Plast. Surg, (2004) 52(5): pp 493-499; discussion p. 500), foot (P. Rosselli, et al., “Use of a soft tissue expander before surgical treatment of clubfoot in children and adolescents,” J. Pediatr. Orthop., (2005) 25(3): pp. 353-356), and calf regions (V. I. Sharobaro, et al., “First experience of endoscopic implantation of tissue expanders in plastic and reconstructive surgery,” Surg. Endosc., (2004) 17(12) p. 513-517).
Hydrogel tissue expanders have been developed for use in the resorbed alveolar ridge, cleft palate (K. F. Kobus, “Cleft palate repair with the use of osmotic expanders: A preliminary report,” Journal of Plastic, Reconstructive & Aesthetic Surgery, (2007) 60: pp. 414-421), and outside the oral cavity (S. J. Bergé, et al., “Tissue expansion using osmotically active hydrogel systems for direct closure of the donor defect of the radial forearm flap,” Plast. Reconstr. Surg., (2001) 108(1): pp. 1-5, discussion pp. 6-7).
Tissue expanders have been used to expand the attached mucosa of the alveolar ridge of resorbed maxillae and mandibles. D. Lew, et al., “Use of a soft tissue expander in alveolar ridge augmentation: A preliminary report,” J. Oral Maxillofac. Surg., (1986) 44(7): pp. 516-519; T. M. Hassan, “Mandibular alveolar ridge augmentation using a soft tissue expander: Report of case,” J. Conn. State Dent. Assoc., (1988) 62(3): pp. 130-134; D. Lew, et al., “An open procedure for placement of a tissue expander over the atrophic alveolar ridge,” J. Oral Maxillofac. Surg., (1988) 46(2): pp. 161-166; A. R. Wittkampf, “Short-term experience with the subperiosteal tissue expander in reconstruction of the mandibular alveolar ridge.” J. Oral Maxillofac. Surg., (1989) 47(5): pp. 469-474; A. A. Quayle, et al., “Alveolar ridge augmentation using a new design of inflatable tissue expander: Surgical technique and preliminary results,” Br. J. Oral Maxillofac. Surg., (1990) 28(6): pp. 375-382; H. C. Schwartz and R. J. Relle, “Extraoral placement of a subperiosteal tissue expander for reconstruction with hydroxylapatite of the severely atrophic mandibular alveolar ridge,” J. Oral Maxillofac. Surg., (1990) 48(2): pp. 157-161; D. Lew, et al., “Use of subperiosteal implants with distal filling ports in the correction of the atrophic alveolar ridge,” Int. J. Oral Maxillofac. Surg., (1991) 20(1): pp. 15-17; D. J. Zeiter, et al., “The use of a soft tissue expander in an alveolar bone ridge augmentation for implant placement,” Int. J. Periodontics Restorative Dent., (1998) 18(4): pp. 403-409; and J. M. Vlassis, et al., “Controlled subperiosteal tissue expansion to facilitate GBR for the placement of endosseous dental implants,” Int. J. Periodontics Restorative Dent., (1999) 19(3): pp. 289-297.
Animal studies have supported these clinical reports. K. Tominaga, et al., “An animal model for subperiosteal tissue expansion,” J. Oral Maxillofac. Surg., (1993) 51(11): pp. 1244-1249; and M. B. Hürzeler, et al., “Guided bone regeneration around dental implants in the atrophic alveolar ridge using a bioresorbable barrier: An experimental study in the monkey,” Clin. Oral Implants Res., (1997) 8(4): pp. 323-331. However, none of these hydrogels can be shaped by the surgeon at the time of surgical insertion.
The Joint Theater Trauma Registry (JTTR) was recently queried for data from United States military injuries from Afghanistan (Operation Enduring Freedom [OEF]) and Iraq (Operation Iraqi Freedom [OIF]) from January 2003 to May 2011. B. A. Feldt, et al., “The joint facial and invasive neck trauma (J-FAINT) project, Iraq and Afghanistan 2003-2011,” Otolaryngol. Head Neck Surg., (2013) 148(3): pp. 403-408. Of the 37,523 discrete facial and penetrating neck injuries that occurred in 7177 service members injured, fracture sites occurred in the maxilla (25%) and mandible (21%). Many of these injuries will require dental restorative procedures that will include dental restorations involving dental implants and intraoral bone grafts.
Metal implants are a standard treatment for the replacement of jaws, teeth, ears, noses, and other parts of the face that have been lost from traumatic injury or disease. Placement of metal implants requires bone for stability and ultimate osseo-integration. When teeth are lost, the mandible and maxilla alveolar bone resorb—a natural phenomenon found in almost every patient. When a mandible or maxilla resorbs, there is often not enough bone for the necessary stability of an implant. Often, bone grafts must be used to replace the lost bone before an implant can be placed. A common problem with the surgical placement of any bone graft—e.g., autogenous, allograft, alloplast, etc. . . . —is inadequate soft tissue to close over the bulk of bone graft material.
Presently, the standard of care uses a silicone “balloon” type of tissue expander. This type of tissue expander requires the periodic injection of fluid (usually sterile saline) into a self-sealing valve to increase the volume of this silicone-type tissue expander. A stem with a valve must be made available through the skin or mucosa from the surgical site where the tissue expander is placed. Often the tissue expander must remain in place for weeks to months until the tissue has been expanded to the desired size.
Although newer designs have reduced complications associated with tissue expanders (R. H. Schuster, et al., “The use of tissue expanders in immediate breast reconstruction following mastectomy for cancer,” Br. J. Plast. Surg., (1990) 43(4): pp. 413-418; S. L. Spear and A. Majidian, “Immediate breast reconstruction in two stages using textured, integrated-valve tissue expanders and breast implants: A retrospective review of 171 consecutive breast reconstructions from 1989 to 1996,” Plast. Reconstr. Surg., (1998) 101(1): pp. 53-63; and J. J. Disa, et al., “The premature removal of tissue expanders in breast reconstruction,” Plast. Reconstr. Surg., (1999) 104(6): pp. 1662-1665), a frequent complication with this type of tissue expander is infection about the exposed surgical area (E. K. Manders, et al., “Soft-tissue expansion: Concepts and complications,” Plast. Reconstr. Surg., (1984) 74(4): pp. 493-507; J. B. McCraw, et al., “An early appraisal of the methods of tissue expansion and the transverse rectus abdominis musculocutaneous flap in reconstruction of the breast following mastectomy,” Ann. Plast. Surg., (1987) 18(2): pp. 93-113; J. Gibney, “The long-term results of tissue expansion for breast reconstruction,” Clin. Plast. Surg., (1987) 14(3): pp. 509-518; J. D. Holmes, “Capsular contracture after breast reconstruction with tissue expansion,” Br. J. Plast. Surg., (1989) 42(5): pp. 591-594; R. H. Schuster, et al., “The use of tissue expanders in immediate breast reconstruction following mastectomy for cancer,” Br. J. Plast Surg., (1990) 43(4): pp. 413-418; and G. P. Pisarski, et al., “Tissue expander complications in the pediatric burn patient,” Plast. Reconstr. Surg., (1998) 102(4): pp. 1008-1012). Moreover, surgical techniques are often modified to accommodate the danger of rupture and bleeding from a tissue expander surgical site. V. I. Sharobaro, et al., “First experience of endoscopic implantation of tissue expanders in plastic and reconstructive surgery,” Surg. Endosc., (2004) 17(12): p. 513-517.
An alternative to tissue expanders to effectively cover bone grafts are surgical techniques which avoid necrosis of the soft-tissue flap covering a bone graft. Tension release of the periosteum, avoidance of the muscles in the flap, and, to a lesser extent, vertical releasing incisions are the primary techniques used in clinical practice. G. Greenstein, et al., “Flap advancement: practical techniques to attain tension-free primary closure,” J. Periodontol, (2009) 80(1): pp. 4-15. Frequently, the oral mucosa used to surgically cover the bone graft dies at the periphery and exposes the graft to all the microbes of the oral cavity, often resulting in loss or partial-loss of the graft. W. Mörmann and S. G. Ciancio, “Blood supply of human gingiva following periodontal surgery. Afluorescein angiographic study,” J. Periodontol, (1977) 48(11): pp. 681-692; and T. N. McLean, et al., “Vascular changes following mucoperiosteal flap surgery: A fluorescein angiography study in dogs,” J. Periodontol, (1995) 66(3): pp. 205-210. Extra soft tissue (skin or mucosa) created by a tissue expander to cover any graft material would provide a significant improvement in clinical therapy.
WO 2007016371 A3 entitled “Readily shapeable xerogels having controllably delayed swelling properties” describes reshapable xerogels with mechanically soft properties. However, Applicants of the present application have made substantial advancements to the technology based on subsequent in vitro and in vivo studies. The novel hydrogel implants of the present invention address a number of problems associated with prior designs. For example, they:                a. are membrane-free and self-swelling;        b. are comprised of non-toxic, biocompatible components;        c. exhibit delayed swelling, so as not to rupture an unhealed incision after emplacement;        d. exhibit controlled swelling, without falling apart, to a maximum size which is less than traditional hydrogels;        e. are elastic when dry, and moldable by a medical practitioner into a smooth shape without sharp edges, which can damage tissue; and                    are robust enough to stay intact throughout the tissue expansion procedure.                        